The task of a programmable controller is to compute the logic status represented by interconnected sensor contacts and to apply the end result of such logic computation to energize or de-energize a transducer or actuator employed in a manufacturing process or, alternatively, to send such result to the outside to control external devices relating such process.
This logic and the interconnected contacts represented thereby are typically illustrated by a diagram. The convention used in such diagram is based on the standard practice used to represent electro-mechanical relay logic and is retained in programmable controller applications because of the widespread familiarity with this type of diagram, commonly termed "a ladder diagram" because each set of logic that corresponds to one output resembles the rung of the ladder. That is, in a ladder diagram, the left and right verticals are the power lines and the horizontal "rungs" are the sets of logic representing the control elements such as interconnected contacts of transducers associated with a particular machine element.
Automated manufacturing equipment frequently employ numerous machine elements such as robot arms, each having several sensors to locate or position the work piece and/or the robot arm with respect to an assembly line or work station. The output signals from these sensors are typically routed across a movable/fixed interface of the robot to a control device. The large wire bundle resulting from the multiplicity of signals is subject to flexure and breakage at the interface between the fixed base and the movable parts of the robot. It is difficult to construct a large cable consisting of many wires which is resistent to breakage resulting from flucture. Although a small number of wires can be formed into a flexible bundle, as for example a coil telephone cord, typical automated manufacturing equipment would require numerous bundles interconnecting the fixed base and the movable parts of the robot which has proven to be unwieldy and expensive in practice.
Alternative methods of wire reduction known in the prior art are based upon the multiplexing of signals from multiple sensors over a single pair of wires on a time share basis. However, such multiplexing inherently introduces transport lag and/or signal timing skew which can adversely affect machine performance and control system complexity. The need to avoid transport lag is particularly acute in high speed operations such as product packaging and bottling operations where faulty product must be rejected in real-time. Furthermore, known prior art approaches are typically extremely expensive, complex and have large package envelopes which are difficult to mount on high speed robot heads.
It will be apparent from a reading of the specification that the present invention may be advantageously utilized in many different machine applications. However, the invention is especially useful when applied to automated robotic equipment used in various high speed manufacturing processes, and will be described in connection therewith.